I encountered a problem animating a three section retractable roof on my stadium. I am trying to animate closing of the roof, but for some reason each section is moving in diefferent speed.

So let me try to explain my current situation:

I have a three section retractable roof. Each section is set 1,90 m in front of the other one because of the wheels. Lets call sections with A, B and C for better understanding. So first all three sections (A+B+C) are moving from frame 1 - 40 by 22 meters. Than section A stops, and other two sections (B+C) continue moving from frame 40 - 80 by 18 meters. And, at the end, sections A and B are staying in place and section C is moving from frame 80 - 120 by 18 meters. Everything looks great and so on but for some reason, during frames 1 - 80, sections of the roof are penetrating into each other. Its like if each sections wants to reach its final location faster than the others, and as a result I get one part of the roof going into the one in front it. So basicly they are not respecting thath initial distance of 1,90 meters they were set at.

I tried grouping them, joining them but nothing... Than it is only OK from frame 1 - 40, but as soon as I separate them to move other two sections, problem appears again. So what I want is to make them move in the same distances they were set initialy at, and just to lose each section at spacing of 40 frames.

So is it possible to edit speed of the objects somehow, parent / child them in some way or is there any other solution.